Influence of Biological Sex and Fitness on Core Temperature Change and Sweating in Children Exercising in Warm Conditions

Purpose: This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., (V) over dotO(2peak)) on the change in gastrointestinal temperature (Delta T-gi) and whole-body sweat rate (WBSR) of children exercising in warm conditions. Methods: Thirty-eight children (17 boys, mean +/- SD = 13.7 +/- 1.2 yr; 21 girls, 13.6 +/- 1.8 yr) walked for 45 min at a fixed rate of metabolic heat production (8 W center dot kg(-1)) in 30(degrees)C and 40% relative humidity. Biological sex and relative (V) over dotO(2peak) were entered as predictors into a Bayesian hierarchical generalized additive model for T-gi. For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for T-gi. Sex, (V) over dotO(2peak), and the evaporative requirement for heat balance (E-req) were entered into a Bayesian hierarchical linear regression for WBSR. Results: The mean increment T-gi for boys was 0.71 degrees C (90% credible interval = 0.60-0.82) and for girls 0.78 degrees C (0.68-0.88). A predicted 20 mL center dot kg(-1)center dot min(-1) higher (V) over dotO(2peak) resulted in a 0.19 degrees C (-0.03 to 0.43) and 0.24 degrees C (0.07-0.40) lower increment T-gi in boys and girls, respectively. A predicted similar to 13% lower body fat in the subsample of girls resulted in a 0.15 degrees C (-0.12 to 0.45) lower increment T-gi. When E-req was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L center dot h(-1) (-0.06 to 0.06), and a 20-mL center dot kg(-1)center dot min(-1) higher predicted (V) over dotO(2peak) resulted in a mean difference in WBSR of -0.07 L center dot h(-1) (-0.15 to 0.00). Conclusions: Biological sex did not independently influence increment T-gi and WBSR in children. However, a higher predicted (V) over dotO(2peak) resulted in a lower increment T-gi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals.